1. Field of the Invention
The present invention relates to an electronic ballast for gas discharge lamps, particularly of a type wherein ballast power output is continuously controllable by way of an adjustment means on the light switch.
2. Description of Prior Art
Ballasts with controllable power output have been previously described, such as in U.S. Pat. No. 4,677,345 to Nilssen; wherein is described a means for controlling the power supplied to a fluorescent lamp by way of controlling the temperature of a pair of saturable current transformers used for determining the frequency in a self-oscillating half-bridge inverter loaded by way of a high-Q series-resonant LC circuit. The higher the temperature, the lower the resulting power output.
However, in an electronic ballast powered from regular electric utility AC power line voltage, prior art does not provide for a control arrangement wherein ballast output power can be controlled by way of applying a control voltage between a control input terminal and one of the power line conductors, where this control input terminal is galvanically connected with the electronic circuitry of the electronic ballast.